Flash apparatus and method



Dec. 29, 1959 H. E. EDGERTON 2,919,383

FLASH APPARATUS AND METHOD Filed June 3, 1957 FIG.2

INVENTOR. HAROLD E.EDGERTON BY ZMM' am ATTORNEYS United States Patent QFLASH APPARATUS AND METHOD Harold E. Edgerton, Belmont, Mass.Application June 3, 1957, Serial No. 663,268

' 14 Claims. (Cl. 315-241) The present invention relates toflash-producing apparatus and methods, and, more particularly, to flashdevices that may be utilized as sources of illumination.

In my co-pending application, Serial No. 588,906, filed June 1, 1956,for Flash Tube and Apparatus, there are disclosed small flash tubes ordevices and appropriate circuits for producing flashes of high-intensityillumination that may be used for suchpurposes as, for example, flashphotography, stroboscopic investigations and, in general, as a source offlash illumination. There are times, however, when extremely simpleapparatus is desirable or even required for producing flash illuminationof high intensity.

The present invention, accordingly, deals with, and has as an object theprovision of, a new and improved and vastly simplified flash apparatusthat, while embodying some of the features of the flash devicesdisclosed in the said copending application, is simpler, less costly andmore readily adapted for-operation at high flash repetition rates.

A further object is to provide a new and improved electric flashapparatus that employs a minimum of electrical components.

An additional object is to provide a new and improved method ofoperating flash devices of this character.

Still a furtherobject is to provide a new and improved flash devicethat, while particularly useful for flash illumination, may also findmore general application where electric energy is to be discharged orflashed througha discharge gap. In summary, the invention, from perhapsits broadest aspect, contemplates a flash device having a pair ofelectrodes inserted with opposite preferably open ends of a normallyinsulative envelope of cross dimension just slightly larger than that ofthe electrodes. Means is provided for rendering the region of thenormally insulative envelope bounding the space between the electrodessubstantially conductive in order to initiate an electric dischargebetween the electrodes within the said space when a voltage is appliedbetween the electrodes. Means is preferably provided for permittingrelative movement of the electrodes to vary the spacing between themwithin the envelope.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in the appended claims.

The invention will now be described in connection with I theaccompanying drawing, Fig. 1 of which is a schematic circuit diagramillustrating a preferred circuit for operating the preferred flashdevice of the present invention, the device being illustrated inlongitudinal cross-section; and Fig. 2 is an explanatory wave-formdiagram.

Referring to Fig. 1, a flash device is shown at 1 having a pair oflongitudinally extending electrodes 3 and 5 which are disposed orinserted within opposite open ends of a normally insulative preferablylight-transparent tubular envelope 7 of inner cross-dimension justslightly larger than that of the electrodes 3 and 5. The electrodes 3 '2and 5 are preferably cylindrical rods of tungsten and the envelope 7 .ispreferably a hollow cylinder of fused quartz or some otherhigh-temperature envelope material that, when the present invention isused for purposes of illumination, is light-transparent at least in theregion bounding the space 15 between the electrodes 3 and 5-.

While the flash device 1, as before stated, may be used for manypurposes, in order to illustrate a preferred application of the same tothe production of successive trains or flashes of light, the apparatusof Fig. 1 is shown of a type embodying alternating-current charging anddischarging circuits. direct-current charging circuits such as thosedescribed in my said copending application and in my United StatesLettersPatent Nos. 2,478,901 and 2,781,707, issued August 16, 1949, andFebruary 19, 1957, respectively, may

also be used. In Fig. 1, the primary winding P of, for

example, a mains-operated transformer 2, is shown cooperating with astep-up secondary winding S. The upper terminal of the winding S isconnected through conductor 4 and a charging resistor R to the upperterminal of one or more energy-storage devices, such as the capacitor orcondenser C, and the lower terminal of the winding S connects byconductor 6 to the lower terminal of the capacitor C, thereby forming acharging circuit. The voltage developed across the capacitor C in thisalternating-current charging circuit will, of course, vary in accordancewith the alternating-current wave form of any type, shown as ofsinusoidal configuration W in Fig. 2.

The flash device 1 is connected in a discharge circuit associated withthe capacitor C, as follows. The upper terminal of the capacitor C isconnected by conductor 9 to the outer end of the electrode 3 and thelower terminal is connected by conductor 11 to the outer end of theother electrode 5. In accordance with the present invention, forpurposes hereinafter described, the conductors 9 and 11, or either oneof them, may be flexible, as shown at 13, so as to'permit the electrodesBrand 5 to be relatively longitudinally moved within the envelope 7 inorder to vary the spacing 15 between the electrodes 3 and 5 within theenvelope 7. Thus, in Fig. 1, an insulative handle 17 is shown rigidlyconnected to the electrode 5 in order to permit the longitudinalinsertion or withdrawal of the same. Similar movement of the electrode 3may, if desired, be effected, though it is suflicient merely to obtainrelative movement of the electrodes 3 and 5,as later explained.

, Assuming, for the moment, that the potential or voltage developed uponthe capacitor C during the charging of the same is suflicient to producea discharge in the space 15 between the electrodes 3 and 5 within theenvelope 7, the discharge will be very rapid and of time durationdependent solely upon the time constant of the discharge circuitcomprising the capacitor C, the conductor 9, the principal electrode 3,the air or other gaseous medium in the space 15, the electrode 5 and theconductors 13 and 11. It is only necessary that the capacitor C chargeto a value suflicient to overcomethe break-down potential between theelectrodes 3 and 5 in order to produce a discharge in the space 15between the electrodes 3 and 5. If the alternating-currentvoltage W is,for example, mains voltage of 60 cycles frequency, the time constant ofthe discharge circuit may be very small compared with the period T ofthe alternating-current voltage. Once the voltage waveform W reachesthethreshold voltage V (point I) at which the space 15 between theelectrodes 3 and 5 may break down, a rapid discharge or flash impulse Iis produced that will terminate very quickly in a time T in view of thesmall time constant of the discharge circuit. As the capacitor Cbecomesrecharged above the threshold value V at successive furtherpoints Patented Dec. 29, 1959 It is to be understood, however, thatprincipal electrodes 3 and very close to the innerwalls.

of the envelope 7, will notbreak down. In order simply to initiate thedischarge process, accordingly, it has been found that one can readilymodify the normally insulative properties of the envelope 7 in theregion bounding the space 15 between the electrodes 3 and 5. In the caseof quartz, before mentioned, it has been found that while the quartz isan excellent insulator at room temperature it can berendered asubstantial conductor upon the ap plication of sufiicient heat thereto.Heat is shown being applied in Fig, 1 to the region of the envelope 7,bounding the space 15 between the electrodes 3 and 5, by a match. It hasbeen discovered that, upon such heating, the region of the envelope wallbounding the space 15 becomes sufficiently conductive to permit thevoltage developed across the capacitor C to initiate a discharge betweenthe electrodes 3 and 5 and thus to start the production of trains offlashes, Fig. 2,- substantially synchronized with, though of greaterfrequency than, the frequency of the alternating current or othervoltage employed in the charging circuit. It has been further found thatthe rendering conductive of the region of the envelope 7 bounding thespace 15 may also be accomplished with the aid of an electrical heater,not shown, and with the aid of a spark-producing member as well. Asanother illustration, if the electrode 5 is inserted into a limitingposition of substantial juxtaposition with the electrode 3, illustratedby the dotted lines in the region 15, then sulficient heat is rapidlygenerated to render the walls of the envelope 7 substantiallyconductive. Upon slightly withdrawing the electrode 5 from the electrode3, accordingly, a discharge is produced in the space 15 which thereafterinitiates the operation illustrated in Fig. 2. The size of the flashingspace 15 is adjustable, by operation of the handle 17, not only toobtain a flashing region of desired dimensions, but, also, to select theelectrode spacing that produces the most regularity in the flashes. Asan illustration, velocity of light measurements have been effected withthe aid of the apparatus of Fig. 1 by monitoring and comparing the timeof transmission of the light pulses and the time of reflection of thesame over a known path length. The electrodes 3 and 5 were tungsten rodelectrodes about 0.04 inch in diameter and the envelope 7 was a fusedquartz envelope tightly fitting about the electrodes .3 and 5.Alternating-current mains voltage was supplied to the primary windingPof the step-up transformer 2, the secondary Winding S of whichdeveloped a voltage of SGilt) volts peak value across a 0.0015microfarad capacitor C through a charging resistor R of 10 ohms. It wasobserved that tungsten oxide is emitted from the open ends of theenvelope? in a continual process during the successive discharges. Notonly is the close proximity of the electrode walls to the inner wall ofthe envelope 7 required for the electrical performance above describedand to limit the flash region to the space only, but this is necessaryto permit of proper relative longitudinal movement of the electrodeswithout play.

Further modifications will occur to those skilled inthe art and all suchare considered to fall within the spirit and scope of the invention asdefined in the appended claims. 1 .What is claimed is;

1. A flash device having, combination, a pair of electrodes insertedwithin opposite. ends of a normally insulative envelope ofcross-dimension slightly larger than that of the electrodes, and meansfor permitting relative movement of the electrodes to vary the spacingbetween them within the enevelope.

2. A flash device having, in combination, a pair of electrodes insertedwithin opposite ends of a normally insulative light-transparent envelopeof cross-dimension slightly larger than thatof the electrodes, and meansfor permitting relative movement of the electrodes from a limitingposition of substantial juxtaposition to vary the spacing between themwithin. the. envelope.

3. A flash device having, in combination, a pair of electrodes insertedwithin oppositeends of a normally insulative envelope of cross-dimensionslightly larger than that of the electrodes, means for rendering theregion of the normally insulative envelope bounding the space betweenthe electrodes substantially conductive in order to initiate an electricdischarge. between the electrodes withinthe. said space when a voltageis applied between the electrodes, and means for permitting relativemove ment ottheelectrodes to vary the spacing between them within theenvelope.

4. A flash device havingnin combination, a pair of electrodesinsertedrwithin opposite ends of a normally insulatiye light-transparentenvelopev of cross-dimension slightly larger. thanthat of theelectrodes, and means for,

rendering the region of the normally insulative envelope bounding, thespace between'the electrodes substantially conductive in order toinitiate an electric, discharge be: tween the electrodes within the saidspace when a voltage is applied between the. electrodes.

5. A flash device having, in combination, a pair of electrodes insertedwithin opposite ends of a normally insulative light-transparent envelopeofcross-dimension slightly larger than that of the electrodes, andmeans, comprising heat-generating means for rendering the region of thenormally insulative envelope bounding the space .between. the electrodessubstantially conductive in order to initiate an electric dischargebetween the electrodes within the said space when a voltage is appliedbetween the electrodes.

6. A flash device having, in combination, a pair of longitudinallyextending electrodes inserted within opposite open ends of alongitudinally extending normally'insulative light-transparent envelopeof cross-dimension slightly larger than that of the electrodes, andmeans for permitting relative longitudinal movement of the electrodes tovary the spacing between them within the envelope. Y

- 7. A flash device having, in combination, a pair of longitudinallyextending electrodes inserted within opposite open ends of alongitudinally extending normally insulative light-transparent envelopeof cross-dimension slightly larger than that of the electrodes, means.for rendering the region of the normally insulative envelope boundingthe space between the electrodes substantially conductive in order toinitiate an electric discharge between the electrodes within the said'space when a voltage is applied between the electrodes, andmeansfor'permitting relative longitudinal movement of the electrodes tovary the spacing between them within the envelope.

8. Flash-producing apparatus having, in combination,

an alternating-current voltage charging circuit including a capacitor, adischarge circuit comprising a flash device having a pair of electrodesinserted within opposite ends of a normally insulativelight-transparent"envelope of cross-dimensionslightlyvlarger than thatof the electrodes, and means for rendering the region of thenormallyinsulative envelope bounding the space between the electrodessubstantially conductive in order to initiate the discharge in thedischarge circuit between the electrodes, the period of the alternatingcurrent being large compared with the tirne comtant of the saiddischarge circuit.

9. A method of operating a flash device having a pair of electrodesinserted Within opposite ends of a normally insulative envelope ofcross-dimension slightly larger than that of the electrodes, thatcomprises, applyinga potential to the electrodes that normally cannotproduce a discharge therebetween, and generating heat in the region ofthe normally insulative envelope bounding the space between theelectrodes to render the said region of the envelope substantiallyconductive, thereby to permit the said potential to discharge betweenthe electrodes.

10. A spark discharge device including in combination, a pair of sparkdischarge electrodes adapted to be connected in a high voltage circuit,and a transparent member open to the atmosphere having an internalcapillary passage in which said electrodes are positioned, saidcapillary passage being vented to the exterior of said transparentmember to provide an escape path into the atmosphere for erosionproducts.

11. A spark discharge device as claimed in claim 10 and in which thereis provided means for permitting relative movement of the electrodeswithin the capillary passage to vary the spacing between them.

12. A spark discharge device as claimed in claim 10 and in which thereis provided means for rendering the region of the capillary passagebounding the space between the electrodes substantially conductive inorder to initiate the spark discharge between the electrodes.

13. A spark discharge device as claimed in claim 12 and in which therendering means comprises heat-producing means.

14. A spark discharge device including in combination, a pair of sparkdischarge electrodes adapted to be connected in a high voltage circuit,a transparent member having an internal capillary passage in which saidelectrodes are positioned, said capillary passage being vented to theexterior of said transparent member to provide an escape path forerosion products, and means for permitting relative movement of theelectrodes within the capillary passage to vary the spacing betweenthem.

References Cited in the file of this patent UNITED STATES PATENTS1,036,884 Mott Aug. 27, 1912 1,799,993 Staege Apr. 7, 1931 2,009,555Mathiesen July 30, 1935 2,078,689 Schneider Apr. 27, 1937 2,137,732Swanson Nov. 22, 1938 2,222,093 Swanson Nov. 19, 1941

